1. Field
Example embodiments relate to a composition for preparing an organic insulator having a crosslinking property, an organic insulator prepared using the same, an organic thin film transistor (OTFT) including the organic insulator, an electronic device including the OTFT and methods of fabricating the same. Other example embodiments relate to a composition for preparing an organic insulator, comprising an organic silane material, a crosslinking agent, and a solvent, an organic insulator prepared using the same, an organic thin film transistor (OTFT) including the organic insulator, an electronic device including the OTFT and methods of fabricating the same.
2. Description of the Related Art
A thin film transistor (TFT), which is primarily used in display devices, may be composed mainly of an amorphous silicon semiconductor, a silicon oxide insulating film, and metal electrodes. To further the diversification of material, an organic thin film transistor (OTFT) using an organic semiconductor has been developed, and has been studied with regard to its applicability. Because the OTFT is flexible and is relatively easy to manufacture, its application to the display field has been accelerated.
Typically, after the development of polyacetylene, which is a conjugated organic polymer having semiconductor properties, organic semiconductors have received attention as an electric and electronic material due to the advantages of organic material, for example, the variety of synthesis methods, relatively easy formability into fibers and films, flexibility, conductivity, and decreased preparation costs, and thus have been studied in the field of functional electronic devices and optical devices. Among devices using such a conductive polymer, research into OTFTs using organic material as an active layer is being conducted. The OTFT may have a structure very similar to a conventional Si-TFT, with the exception that the semiconductor region thereof is formed using an organic material, instead of Si. Such OTFTs are advantageous because a semiconductor layer may be prepared through a printing process under atmospheric pressure, rather than a plasma-enhanced chemical vapor deposition process, which is the conventional silicon process, and because it is possible to perform a roll-to-roll process using a plastic substrate, thereby decreasing the cost of fabricating the transistor.
Further, the OTFTs have charge mobility equal to or higher than amorphous Si-TFTs, but their operating voltage and threshold voltage may be relatively high. Where pentacene is used along with amorphous silicon (SiO2), charge mobility may be realized to the level of about 0.6 cm2/V·sec, suitable for actual use. However, an operating voltage of about 100 V or more and a sub threshold voltage about 50 times higher than in the case of amorphous silicon are undesirably required. Among the properties of TFTs, in order to control the operating voltage and decrease the sub threshold voltage, various attempts have been made to apply an insulating film having a high dielectric constant (high k) to OTFTs, as well as Si-TFTs. For example, the use of a ferroelectric insulator, including BaxSr1-xTiO3 (BST), Ta2O5, Y2O3, and TiO2, and an inorganic insulating film with a dielectric constant of about 15 or more, including PbZrxTi1-xO3 (PZT), Bi4Ti3O12, BaMgF4, SrBi2(Ta1-xNbx)2O9, Ba(Zr1-xTix)O3 (BZT), BaTiO3, SrTiO3, and Bi4Ti3O12, has been disclosed. In the devices using the above-mentioned material, the insulating materials are applied using a deposition process (e.g., CVD, sputtering and/or ALD) or a sol-gel process, and the properties of the device, having a charge mobility of about 0.6 cm2/V·sec or less and threshold voltage of about −5 V or less, have been reported. However, because most of the device fabrication process is performed at increased temperatures (about 200° C.˜about 400° C.), the use of various substrates may be restricted, and applying a printing process may be difficult. Although an organic insulating film using polyimide, BCB (BenzoCycloButene) or photoacryl has been proposed, the device properties exhibited may not be desirable to the extent of substituting for inorganic insulating films.
While the OTFT is applied not only to LCDs but also to devices for driving flexible displays using organic EL, a charge mobility of about 10 cm2/V·sec or more is required. In the manufacturing process, methods using an all-printing process or an all-spin-on process on a plastic substrate are being studied. Research is being directed toward an organic insulator in which conditions favorable for forming an organic active layer are provided, along with a relatively simple preparation process, to thus enlarge the grain size of the organic active layer, resulting in increased charge mobility, upon application to devices in place of inorganic insulating films. There are reports of charge mobility of about 1˜5 cm2/V·sec. However, such organic insulating films generally have a dielectric constant of about 3˜4 and require an increased operating voltage (about 30 V˜about 50 V) and threshold voltage (about 15 V˜about 20 V).
With the goal of increasing the dielectric constant of the organic insulator, a method of dispersing nano-sized ferroelectric ceramic particles in an insulating polymer is disclosed in the related art. However, the above method is undesirable because the ceramic particles negatively affect the formation of the organic active layer, and thus charge mobility may be decreased, and also leakage current may be increased, undesirably causing problems in which the above material should be provided in the form of a double structure along with an organic material having improved insulating properties.
In addition, upon the fabrication of OTFT devices, a multilayered structure and pattern may be formed using organic and inorganic materials. In FIG. 1, a conventional organic thin film transistor may include a gate electrode 2 formed on a substrate 1, and an insulating film 3, source/drain electrodes 4,5 and a semiconductor layer 6 are formed thereon. As such, there is a need for an insulating layer which is present as a crosslinked dense film so as to be resistant to chemicals and process conditions in the subsequent processing of the insulating film. For example, an insulator having an improved crosslinking property needs to be realized. However, a conventional crosslinking agent, mainly used for crosslinking the silane resins, may function to form a chemical bond between Si—OH groups or to chemically bind to Si—OH, and limitations may be thus imposed on increasing the crosslinking property.